There are many situations in which a user at a remote location wishes to receive updated information that is specifically tailored to the user's needs. For example, an aircraft pilot may require a current weather map or aeronautical chart for a specific flight path before beginning a flight, or the crew of an ocean-going vessel may require an updated nautical chart showing local harbor anchorages, entrances, channels or the like. Similarly, hikers, skiers and other individuals engaged in outdoor sporting activities may wish to obtain current topographical maps of the local region in which the activity will take place.
Typically, nautical charts and topographical maps are made available in hard copy form and are updated on a relatively infrequent basis. Weather maps (for which frequent updating is essential) have in some cases been made available to pilots and others by facsimile or modem, but the requirement for access to a facsimile machine or computer may prevent the user from obtaining updated weather maps as frequently as might be desired. Moreover, in all of these cases, the maps are generally designed to cover a wide geographic area and are not tailored to the needs of any specific user.
There currently exists a satellite-based position determination system known as the Global Positioning System (GPS), in which a number of satellites in orbits above the earth broadcast precise timing signals that can be received by mobile receivers in aircraft, ships and land vehicles to provide position information using triangulation techniques. In addition to providing latitude and longitude information, GPS receivers often use various types of onboard data storage devices (such as disks and cartridges) to provide map displays that are combined with the satellite-derived GPS position data. This allows the position of the user to be shown graphically on a moving map, for example. While these receivers are very useful for navigation, the map data must be updated frequently (typically by obtaining new disks or cartridges through a subscription service) in order to remain useful. Even with frequent updating, some types of map data (such as weather map data) cannot be effectively provided in this way.